Power = Power Opp and Damage = Damage Opp only copy the power or damage that is printed on the other card. This is before abilities and bonus are applied. For example, if you try to use a Power = Power Opp card against Copper, you'll only get 4 power, then modified by your bonus if appropriate.
Damage = opp damage always copy the basic number printed on the card, before any modification
so if you have La Junta VS 4 damage card, and your opp has +3 damage (Shogunn) you will only copy 4 damage, not 7 damage
the same applies with copy opp bonus too
as you can see, you will only copy 4 damage and +2 damage from La Junta bonus which makes you have 6 damage
your opp will have 4 damage +2 damage from copy opp bonus which also makes them have 6 damage